The present invention relates to a quality control method for a machine for producing packaging.
There are various types of processing machines used for producing packaging: for example some of these machines process strips, printing them then cutting them into individual copies. Others process sheets by printing them, including possibly by stamping, and others still convert printed sheets by cutting them into individual copies. Finally, some machines have the task of folding and gluing individual copies. The materials of which the strips or sheets are made may be paper or cardboard, or even a plastic.
Quality control systems exist which are able to detect the presence of defects on all the objects converted by a machine, whether these be sheets or individual copies. Depending on the type of machine, quality control may be carried out during the conversion process, for example after a printing process but before a cutting process performed in the same machine, or alternatively may be carried out at the end of the conversion process, for example in the case of machines which do nothing more than print sheets without cutting them, such as specialist machines for stamping and applying metalization. Or alternatively it may be formed at the entry to the machine, for example to check the quality of the individual copies entering a folder-gluer. Usually, the presence of a defect results in the non-conforming object being ejected.
The existing quality control systems are based on a method that involves acquiring a reference image then acquiring, for each object the quality of which is to be controlled, an image that is compared against the reference image. Conventional image processing programs allow this comparison to be made and the defects thus to be detected.
The useful surface to be quality-controlled may vary according to the type of object being quality-controlled, sheet or individual copy. For example, in the case of a printed sheet that will later be cut into a number of individual copies, a defect might be detected in a part of the sheet which will not form part of an individual copy, but which will become waste. The presence of such a defect must not result in the quality-controlled object being rejected, because the defect will ultimately no longer be present in the actual packaging.
In order to avoid detecting defects in zones that are not relevant, certain quality control methods involve a step of defining masked zones. Before being able to begin a conversion job on the machine, the user of the machine manually defines those zones that are not relevant, known as masked zones, using the reference image. These zones are usually basic geometric shapes, for example polygons or ellipses. Once all of the masked zones have been defined by hand, the set is saved either in the form of a model that defines only the geometry of all the masked zones and their position within the image, or in the form of a file known as a job file which contains not only the model, but also all the parameters needed for performing quality control. For example, the job file may contain the reference image, data regarding the brightness of the lighting, or data regarding the sensitivity of the camera.
In the existing quality control methods, this step of defining the masked zones is performed directly on the machine.
Once the phase of defining the masked zones has been completed, the user can go on to convert a set of objects, by performing quality control on each one of them without defects being detected in zones that are not relevant, because these zones have been defined as masked zones. When he wishes later to convert another set made up of the same elements, he will not have to repeat the phase of defining the masked zones—all he will need to do is use the job file, or at least the model defined earlier.
Nevertheless, defining a new job of work is a lengthy and painstaking process. The technical problem addressed by the invention is therefore that of making the defining of a new job of work quicker and easier.